1. Field of the Invention
This invention relates to the communication of optical Gigabit Ethernet signals from multiple Gigabit Ethernet optical transceiver interfaces directly to an array of Gigabit Ethernet receivers and lasers integrated on an optoelectronic-VLSI (Very Large Scale Integration) chip. More particularly, this invention relates to the delivery of several hundred (or more) Gigabit Ethernet optical signals using a fiber bundle to a chip containing several hundred (or more) parallel Gigabit Ethernet optical transceivers.
2. Description of the Related Art
As is known and understood, 850 nm Gigabit Ethernet (GbE) optical links are currently implemented with discrete transceivers over graded-index multimode fibers. To achieve multiple Gigabit Ethernet links, multiple discrete transceivers, of necessity, have to be used with individual separate fibers, either packaged into individual fiber ferrules or in one-dimensional arrays.
Analysis has shown, however, that several issues have to be resolved before optoelectronic-VLSI technologies can be used to provide such Gigabit Ethernet compliant links. For example, because multimode fibers can support many different propagating modes along the length of the fiber, there exists a potential for interference between such modes. This has been determined to lead to either constructive or destructive interference between the modes, resulting in a speckle pattern at the detector that shifts and changes when the amount of light coupled into each mode group varies as a result of fluctuations in the spectrum of the source, changing environmental conditions, vibration, etc. In an attempt to suppress this modal noise, large-area multi-transverse-mode vertical cavity surface emitting lasers (VCSELS) have been employedxe2x80x94but, such emitters are difficult to integrate in large arrays, because such VCSELS typically require larger operating currents, and hence have higher power dissipation.
To be useful for data networking applications, furthermore, each transceiver must conform to one of the standardized data transmission formats. Amongst the most recent is the new IEEE-approved Gigabit Ethernet standard where the data transmission rate for a single GbE channel is 1.25 Gigabits-per-second. Such standard provides for optical transmission over 50 um core-size as well as 62.5 um core-size graded-index multimode fibers at a wavelength of 850 nm. Trying to make an array of hundreds (and more) of multimode graded-index fibers arranged into a two-dimensional fiber bundle, however, has proven to be quite inefficient using present technology. While arrays of multimode step-index fibers are able to be manufactured efficiently, the step-index fibers do not meet the GbE standard for optical transmissionxe2x80x94and, primarily, because of the modal noise problem.
As will become clear from the following description, with the present invention, a new and improved system results which provides parallel communication between multiple discrete Gigabit Ethernet optical transceivers and an optoelectronic-VLSI chip containing hundreds (or more) of optical transceivers using a fiber-bundle composed of these step-index fibers. Power dissipation on the chip will be seen to be reduced by using power-efficient vertical cavity surface emitting lasers, and modal noise will be seen to be prevented from deteriorating the link by the utilization of standard Gigabit Ethernet graded-index fiber jumpers between each individual transmitter interface and the fiber bundle on the one hand, and between each individual receiver interface and the corresponding integrated laser on the other hand. In particular, and as will be seen, the step-index fibers are selected of a core size and numerical aperture to insure that substantially all of the light coupled from each transmitter interface into a standard Gigabit Ethernet 50 um graded-index fiber jumper will be captured by the corresponding step-index fibers in the bundle and delivered to the corresponding detectors on the optoelectronic-VLSI chip in a power efficient manner. At the same time, a standard Gigabit Ethernet 62.5 um graded-index fiber jumper is employed between each individual receiver interface and the corresponding integrated laser to insure that substantially all of the light coupled into the step-index fiber from the integrated lasers will be captured by the corresponding 62.5 um jumper and delivered to the corresponding individual receiver interface.
In a preferred embodiment of the invention, such step-index fiber bundle was selected with a core size varying from 50 um to 60 um, and with an effective numerical aperture between 0.19 and 0.25, effectively greater than the numerical aperture of the 50 um graded-index fiber jumper and less than the numerical aperture of the 62.5 um graded index fiber jumper. By relaxing the constraints on the core size of the step-index fibers, the step-index fiber bundle becomes easier to manufacture and also reduces its cost.
As will be appreciated by those skilled in the art, a stepindex fiber bundle arrayxe2x80x94which can be fabricated using present-day technologiesxe2x80x94, in this manner, can be employed in supporting the Gigabit Ethernet standard for graded-index fibers in optical communication, thus allowing for integration of a large number of transceivers onto a single chip.